A tão aguardada ‘pílula anticoncepcional masculina’, capaz de evitar que o homem engravide a mulher, pode estar mais perto de chegar às farmácias. Cientistas australianos anunciaram que descobriram uma forma de interromper a liberação de espermatozóides de forma reversível, sem afetar o desempenho sexual.
Testes realizados em ratos comprovaram a eficácia da pílula e os animais não sofreram efeito colateral. Após a interrupção do medicamento, eles voltaram a produzir prole normalmente.
A pílula apaga geneticamente duas proteínas (alfa1A-adrenérgico e P2X1-purinoceptor), capaz de bloquear a liberação de espermatozoides durante o ato sexual.
Testes anteriores com pílulas anticoncepcionais alteravam o sistema hormonal. Os testes realizados em ratos mostravam efeitos colaterais.
A 1929 investigation in Jiangxi showed correlation between low fertility in males and use of crude cottonseed oil for cooking. The compound causing the contraceptive effect was determined to be gossypol.
In the 1970s, the Chinese government began researching the use of gossypol as a contraceptive. Their studies involved over 10,000 subjects, and continued for over a decade. They concluded gossypol provided reliable contraception, could be taken orally as a tablet, and did not upset men’s balance of hormones.
However, gossypol also had serious flaws. The studies also discovered an abnormally high rate of hypokalemia among subjects.
Hypokalemia — low blood potassium levels — causes symptoms of fatigue, muscle weakness, and at its most extreme, paralysis. In addition, about 7% of subjects reported effects on their digestive systems, and about 12% had increased fatigue. Most subjects recovered after stopping treatment and taking potassium supplements. The same study showed taking potassium supplements during gossypol treatment did not prevent hypokalemia in primates. The potassium deficiency may also be a result of the Chinese diet or genetic predisposition.
In the mid-1990s, the Brazilian pharmaceutical company Hebron announced plans to market a low-dose gossypol pill called Nofertil, but the pill never came to market. Its release was indefinitely postponed due to unacceptably high rates of permanent infertility. 5-25% of the men remained azoospermic up to a year after stopping treatment. The longer the men had taken the drug and the higher their overall dosages, the more likely they were to have lowered fertility or to become completely infertile.
Researchers have suggested gossypol might make a good noninvasive alternative to surgical vasectomy.
In 1986, the Chinese stopped research because of these side effects.
In 1998, the World Health Organization’s Research Group on Methods for the Regulation of Male Fertility recommended the research should be abandoned. In addition to the other side effects, the WHO researchers were concerned about gossypol’s toxicity: the toxic dose in primates is less than 10 times the contraceptive dose. This report effectively ended further studies of gossypol as a temporary contraceptive, but research into using it as an alternative to vasectomy continues in Austria, Brazil, Chile, China, the Dominican Republic, and Nigeria.
(texto de: Wikipédia)